Tubby means round and plump in shape, like a tub. The word can describe someone who is short and chubby, with a rounded belly. Picture a bear that's been eating plenty of food before winter: round, well-fed, and solid.

Just as a tub has a wide, rounded shape, someone described as tubby has that same kind of roundness. You might see it used in older children's books to describe a character who is pleasantly plump and comfortable-looking, but it can also sound unkind if you use it about a real person.